How superconducting sheets could reflect gravitational waves

March 7, 2009

How superconducting sheets could reflect gravitational waves

University of California scientists propose a new kind of mirror that reflects gravitational waves and may even convert them into electromagnetic waves.

Gravitational waves are the elusive distortions in spacetime created by the universe’s most violent events-collisions between black holes, stars exploding and even the big bang itself.

Nobody has bagged a confirmed sighting of these waves but that may change thanks to an intriguing idea from Raymond Chiao and pals at the University of California, Merced. They propose the existence of a new kind of mirror that reflects gravitational waves and may even convert them into electromagnetic waves.

First some background. Theoretical physicists have long noticed that in certain circumstances, Einstein’s equations of general relativity, which predict the existence of gravitatonal waves, bear a remarkable similarity to Maxwell’s equations that describe the behaviour of electromagnetic radiation. That’s an important clue for understanding how gravitational waves behave, says Chiao.

He points to the specific case in which a thin superconducting film reflects em waves. If that works for em waves, then the mathematics indicates that it must also work for gravitational waves.

Here’s the thinking. A gravitational wave stretches and squeezes space as it moves through the universe. Any object in its way will appear to be squashed and stretched in the same way, the particles within this object will move with the distorted space in a specific trajectory (called geodesic motion).

The new idea comes from considering what happens to a superconducting sheet when a gravitational wave passes by. The Cooper pairs within the sheet are quantum objects governed by the uncertainty principle and so cannot have specific trajectory: they are entirely delocalised. On the other hand, the ions that make up the crystal structure of the superconductor are not delocalised and so can move along a geodesic trajectory when a gravitational wave passes.

This is the basis on which a gravitational wave can interact with a superconducting sheet. “Quantum delocalization causes the Cooper pairs of a superconductor to undergo non-geodesic motion relative to the geodesic motion of its ionic lattice,” says Chiao and buddies.

They speculate that this difference in motion causes the sheet to absorb energy from the gravitational wave and then re-radiate it as gravitational wave travelling in the opposite direction-in other words specular reflection.

That’s an extraordinary claim which needs some further investigation, not least because there’s a fair amount of disagreement over the GR-Maxwell link in the first place.

Nevertheless, Chiao and co go even further by ending their paper with this:

“This implies that two charged, levitated superconducing spheres in static mechanical equilibrium, such that their Coulombic repulsion balances their Newtonian attraction, should be an efficient transducer for converting EM waves into GR waves and vice versa. A Hertz-like experiment in which a transmitter and receiver of GR microwaves are constructed using two such transducers should therefore be practical to perform.”

So a pair of levitating, superconducting spheres would act as an antenna for gravitational waves and convert them into electromagnetic waves.

Why wait for LIGO? What’s the betting that superconducting spheres can make the detection first?